end of the electrolysis the current is lowered, the rotation stopped and the
usual washing and drying of the cathode effected.
Dissolution of the Metallic Deposits.—Deposits of copper, zinc,
nickel, silver, etc., are dissolved in nitric acid ; tin and iron in hydrochloric
acid ;' antimony in nitric acid containing a little tartaric acid in solution ;
lead peroxide in nitric acid with a little oxalic acid dissolved in it ; rnan-
ganous-manganic oxide in dilute sulphuric acid containing hydrogen peroxide,
When Winkler electrodes are used, it is very convenient to immerse them
in a tall, narrow vessel fitted with a ground stopper and containing the
proper acid, which may be used repeatedly.
COPPER AND ITS ALLOYS
The more important commercial products are : refined and electrolytic
copper and its various alloys with phosphorus, silicon, manganese, zinc,
tin and nickel.
After the usual tests for industrial copper, methods for the analysis of
its principal alloys will be given, beginning with alloys of copper with phos-
phorus, silicon and manganese, and coming later to the most important
ones, namely, the ordinary and special brasses and the ordinary and special
Alloys of copper with nickel and zinc (argentan) will be treated along
with nickel and its alloys, and its alloys with tin and antimony (anti-friction
metals) along with tin and its alloys.
The complete analysis of commercial copper, that is, the determination
of the copper and of ah1 the extraneous elements accompanying it in large
or small proportions (Bi, Pb, Sb, As, Sn, Ag, Au, Fe, Ni, Co, Zn, S, Se,
Te, C, P, Si, 0, etc.) is a very long and delicate operation.1 Beyond a
determination of the copper, commercial analyses as a rule require only
estimations of the more injurious elements, especially of bismuth, arsenic,
phosphorus, antimony, lead, sulphur, nickel, iron and oxygen. Rapid
and exact methods for determining these elements will, therefore, be given.
1. Determination of the Copper (by electrolysis}.—5 grams of
the metal in fine turnings, freed from fat by means of ether and from traces
of iron from the sampling tool by means of a magnet, are placed in a tall,
narrow beaker covered with a clock-glass or with an inverted funnel of
rather less diameter than the mouth of the beaker. The metal is there
covered with water and treated with 5-7 c.c. of cone, sulphuric acid and
15-20 c.c. of nitric acid (D 1-33), gentle heat being applied towards the
end of the action. Refined copper usually dissolves, but unrefined metal
may leave a residue and traces of copper occluded in the latter must be
extracted by boiling. In either case the unfiltered liquid is made up to
1 See Hampe : Chem. Zeit., 1893, XVII, p. 1678 ; Fresenius : Quantitative Analysis ;
A. Hollard: Chem. Zeit., 1900, XXIV, p. 146.le or otherwise, while at the same time the liquid